Aspects of the invention can relate to an image quality improvement technology of an image display apparatus. More specifically, aspects of the invention can relate to an optical configuration suitable for realizing expansion of dynamic range of display brightness and high gradation.
Image quality improvement in related art electronic display apparatuses, such as an LCD (Liquid Crystal Display), an EL (Electro-luminescence) display, a plasma display, a CRT (Cathode Ray Tube), and a projector can be remarkable and an apparatus having performances comparable to the human visual properties can be realized with respect to resolution and color gamut. However, with respect to the brightness dynamic range, its reproduced range remains on the order of 1 to 102 [nit], and further, the number of gradations is generally 8 bits.
On the other hand, the human visual perception provides a brightness dynamic range that can be perceived at a time is on the order of 10−2 to 104 [nit], and further, the brightness discriminative ability is on the order of 0.2 [nit]. This is said to be equal to 12 bits in terms of number of gradations. Seeing a display image of a current display apparatus through such visual properties, the human does not satisfy the reality and impact because the narrowness of the brightness dynamic range stands out and additionally, the gradations in shadow parts and highlight parts are insufficient.
Further, in computer graphics (CG) used for movies or games, the movement for pursuing description reality by providing display data (hereinafter, referred to as “HDR (High Dynamic Range) display data”) with brightness dynamic range and gradation characteristics close to human visual perception is becoming the mainstream. However, there is a problem that powers of expression the CG contents originally have can not be exerted sufficiently because the performance of the display apparatus for displaying CG is insufficient.
Furthermore, in the next OS (Operative System), 16-bit color space is planned to be adopted, and the brightness dynamic range and the number of gradations will be increased dramatically compared to those in the current 8-bit color space. Accordingly, the demand for realization of an electronic display apparatus with high dynamic range and high gradation capable of utilizing the 16-bit color space is expected to be increased.
Among related art display apparatuses, projection display apparatuses (projectors), such as a liquid crystal projector and DLP (Digital Light Processing, registered trademark) projector, can perform large screen display and are effective apparatuses for reproducing the reality and impact of display images. In this field, the following proposals have been made in order to solve the above described problems.
As a display apparatus with high dynamic range, for example, there is a technology disclosed in, for example, Japanese Patent Application Publication 2001-100689. In the technology, a light source, a second light modulator device for modulating brightness of all wavelength regions of light, and a first light modulator device for modulating the brightness of the wavelength regions with respect to respective wavelength regions of RGB three primary colors of the wavelength regions of light are provided for forming a desired brightness distribution by modulating light from the light source by the second light modulator device, imaging the optical image thereof onto a display surface of the first light modulator device and performing color modulation, and projecting the secondary modulated light. The respective pixels of the second light modulator device and the first light modulator device are separately controlled based on the first control value and the second control value determined from the HDR display data, respectively. As the light modulator device, a transmittance modulator device having a pixel structure or segment structure with independently controllable transmittances and capable of controlling a two-dimensional transmittance distribution is used. As a representative example thereof, a liquid crystal light valve can be cited. Further, a reflectance modulator device may be used in place of the transmittance modulator device, and as a representative example thereof, a DMD (Digital Micromirror Device) can be cited.
Now, the case of using a light modulator device having a transmittance of dark display of 0.2% and a transmittance of bright display of 60% is considered. Regarding the light modulator device alone, the brightness dynamic range is 60/0.2=300. The display apparatus corresponds to the case where light modulator devices having the brightness dynamic range of 300 are optically and serially arranged, and thereby, the brightness dynamic range of 300×300=90000 can be realized. Further, the equal way of thinking is held with respect to the number of gradations, and the number of gradations exceeding 8 bits can be obtained by optically and serially arranging light modulator devices with 8-bit gradation.
However, in the technology of the Publication 2001-100689, since an optical image formed by one optical modulator device is transmitted to the other optical modulator device using an optical element for illumination system having large optical aberration, there is a problem that illumination light having a desired light intensity distribution is difficult to be transferred onto the other optical modulator device accurately.